This invention is directed to reading and writing data residing on flat media, and more particularly to read/write heads used for reading and writing data on flat rotating media.
Reading and writing data to and from flat rotating media requires a read/write head be configured to xe2x80x9cflyxe2x80x9d above the media on an actuator arm, deriving a signal that is then electrically processed by a preamplifier (preamp) mounted on or proximal a base of a disc drive supporting the actuator arm. This arrangement is beneficial because it is desired to keep the weight of the head to a minimum to insure flying with no contact to the media; or if there is contact to insure that as little damage occurs as possible.
As data has become steadily denser and more speed is required, tolerances have become ever closer. Since very high tolerances are routinely maintained in the semiconductor industry, the art has begun to rely on that industry for the light weight, close tolerance heads that are needed.
Initially, the presumption was that polycrystalline silicon would be most advantageous, for several reasons. Polycrystalline silicon (poly) is known to etch more readily in many cases, and the resistivity, in this case the tendency to create leakage paths, may more easily be increased to avoid or reduce leakage currents.
Recently the speeds desired for read/write heads has increased to the point that parasitics associated with the connections from the head to the location of the preamp have become a problem, limiting the rise and fall times of signals and creating a limit on performance thereby.
A particular concern is the wiring from the preamplifier (preamp) output to a coil used for writing. While at this time the preamplifier output wiring contributes only 30 percent of the total degradation of the write flux rise time, the contribution is increasing, and the contribution of flex wiring to the degradation of write flux rise time is a potential bottle neck.
The present invention will be seen to provide a solution to this and other problems, such as the cost of the preamp.
For high density-high data rate writing of data to magnetic data media, the starting material for a read/write head being made from a semiconductor material is selected from monocrystalline semiconductor grade stock, preferably silicon. The semiconductor material is formed from semiconductor on insulator (SOI) for improved isolation prior to head fabrication. Isolation of the read/write head allows the head to function in noisy environments, where electrical noise is introduced to the main structures, such as the flexure, which could act as an antenna for such noise.
SOI may be a high temperature process, but is fully compatible with the lower temperature steps that follow, since the high temperature steps form the base material and the following steps, such as defining the preamp, only modify the completed base material. Examples of semiconductor grade stock are materials such as silicon, various compounds of gallium such as gallium arsenide, germanium, germanium on silicon, and potentially silicon carbide and diamond, though many other semiconductor and semiconductor compounds are known and could be used. Note that silicon carbide and diamond, because of the hardness of these materials, are especially attractive, though not presently considered practical for use.
Recognizing that the material thereby has the capability of having semiconductors formed thereon with a semiconductor process without adding a weight or size penalty, at least a preamp circuit is defined in the material. The preamp, optionally along with other functions such as filtering and signal processing, is located such that no damage will result in the subsequent processing, and isolated by methods commonly known in semiconductor processing as SOI technology, as discussed before. Surface protection can be provided, for example, by depositing an overcoat of protective material over the preamp and the related circuits, which is then planarized to provide for a conventional read/write head build. Multiple preamps can be built around a single head element and connected through a selective via process to save cost. The via process for interconnecting the various conductors can be shared by the preamp and the read/write head if cost justifies it.
The write head inductance seen by the preamp determines the write flux time. This inductance is composed of the inductance from the head yoke, head coil, and flex wire. Currently the flex wire inductance contribution to write flux degradation is about 30 percent of the total. With the demand for high density/high data rate operation, the desirable write flux time is approaching 2 nanoseconds. Therefore, the high current connections from the preamp to the coil are made as short as the present technology allows, and much faster rise and fall times are possible thereby. In fact, the contribution to write flux rise time is substantially eliminated by this invention.
Additionally, if differential outputs are provided by the preamp, the power for writing to a given coil from a given power supply is substantially doubled without requiring additional external connections, and especially external connections requiring high rise and fall time currents. Conventional approaches to solve the problem of write flux rise time may use the flex wire and/or the preamp in suspension. Both methods improve rise time, but have had limited success, since the flex wire inductance is about 0.5 to 0.7 nanohenries per millimeter, and there are physical limits to how close a discrete preamp can be moved to the head.